Lower alkane oxidative dehydrogenation catalysts and a process for producing olefins

ABSTRACT

The invention provides catalysts for oxidative dehydrogenation of lower alkanes, said catalysts being suitable for use in vapor phase oxidative dehydrogenation of C 2 -C 5  lower alkanes in the presence of molecular oxygen to produce corresponding olefins and characterized by having a composition expressed by a general formula (I) below:  
     Mn α E 1   β E 2   γ O x   (I)  
     (in which Mn denotes manganese, and O, oxygen; E 1  is at least one element selected from the group consisting of P, As, Sb, B, S, Se, Te, F, Cl, Br, I, Nb, Ta, W, Re and Cu; E 2  is at least one element selected from the group consisting of Cr, Fe, Co, Ni, Ag, Au, Zn, Tl, Sn, Pb, Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Y, La, Ce, Nd and Sm; and α, β, γ and x denote atomic numbers of Mn, E 1 , E 2  and oxygen, respectively, where when α=1, β=0.01-10, γ=0-5, and x is a numerical value determined by the state of oxidation of those elements other than oxygen).  
     When these catalysts are used in reactions for oxidizing and dehydrogenating C 2 -C 5  alkanes with molecular oxygen at vapor phase, corresponding olefins can be produced at high yield.

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS

[0001] This invention relates to lower alkane oxidative dehydrogenationcatalysts and a production process of olefins using said catalysts. Morespecifically, the invention relates to the catalysts which are suitablefor use in vapor phase oxidative dehydrogenation of C₂-C₅ lower alkanes(hereinafter occasionally referred to simply as “lower alkanes”) in thepresence of molecular oxygen to produce corresponding olefins, and aprocess for oxydizing and dehydrogenating lower alkanes with molecularoxygen to produce corresponding olefins at high yields, with the use ofsaid catalysts.

[0002] The invention also relates to a process for producing, from theolefins which have been obtained through vapor phase oxidativedehydrogenation of C₂-C₅ lower alkanes in the presence of molecularoxygen, the corresponding unsaturated aldehydes and/or unsaturatedcarboxylic acids.

PRIOR ART

[0003] As a production process for lower olefins, in particular,propylene and isobutene, simple dehydrogenation process of lower alkanesis recently reduced to industrial practice. However, this process issubject to an essential problem that it is incapable of giving highconversion due to the equilibrium limitation and furthermore requireshigh temperatures. Still in addition, deterioration of the catalystwithin a short period is inavoidable in said process, which necessitatesfrequent regeneration of the catalyst using a switch converter or thelike. In consequence, plant construction costs and utility costs forrunning the process are high and, depending on the conditions oflocation, it is unprofitable and its industrial application isrestricted.

[0004] Whereas, attempts to produce lower olefins from lower alkanesthrough oxidative dehydrogenation which is free from the limitation byequlibrium have been made since long, and various catalyst systemstherefor have been proposed. Among those known, there are Co-Mo oxidecatalyst (U.S. Pat. No. 4,131,631), V—Mg oxide catalyst (U.S. Pat. No.4,777,319), Ni—Mo oxide catalyst (EP 379,433 A1) CeO₂/CeF₃ catalyst (CN1,073,893A), Mg—Mo catalyst [Neftekhimiya (1990), 30(2) 207-10],V₂O₅/Nb₂O₅ catalyst [J. Chem. Commun. (1991) (8) 558-9], rare earthvanadates catalyst [Catal. Lett. (1996), 37, (3,4), 241-6] andB₂O₃/Al₂O₃ catalyst [ACS Symp. Ser. (1996), 638 (HeterogeneousHydrocarbon Oxidation) 155-169). Those known catalysts, however,invariably show very low level oxidative dehydrogenation performance,the property of the prime importance, and are far short of industrialpractice.

[0005] Japanese Laid-open (KOKAI) Patent Application, KOKAI No.245494/1996 furthermore contains a disclosure on a process for furtheroxidizing propylene, which was formed through dehydrogenation ofpropane, to produce acrylic acid. This process, however, necessitatesremoval of the hydrogen formed during the dehydrogenation of propanefrom the reaction gas. Japanese KOKAI Nos. 045643/1998, 118491/1998,62041/1980 and 128247/1992, etc. disclose processes for formingunsaturated aldehydes and/or acids from lower alkanes, in particular,acrolein and/or acrylic acid from propane and methacrolein and/ormethacrylic acid from isobutane. However, yield of these object productsindicated in these publications are very low, and the processes need tobe improved in various aspects including the catalyst to be used.

THE PROBLEM TO BE SOLVED BY THE INVENTION

[0006] An object of this invention is to provide novel oxidativedehydrogenation catalysts useful for vapor phase oxidativedehydrogenation of lower alkanes with molecular oxygen to producecorresponding lower olefins at high yield; and also to provide a processfor producing from lower alkanes the corresponding olefins at highyield, by the use of said catalysts.

[0007] Another object of the invention is to provide a process forproducing from lower alkanes corresponding unsaturated aldehydes and/orunsaturated carboxylic acids at high yield.

MEANS FOR SOLVING THE PROBLEM

[0008] We have made concentrative studies in search of the catalystssuitable for oxidizing and dehydrogenating lower alkanes with molecularoxygen to produce the corresponding lower olefins, to discover that acatalyst containing manganese as the indispensable component, or acatalyst in which said catalytically active component is supported on arefractory inorganic carrier exhibit excellent oxidative dehydrogenationperformance; and that lower olefins could be produced at high yield withthe use of said catalyst. The present invention has been completed basedon these discoveries.

[0009] Thus, the present invention provides catalysts for oxidativedehydrogenation of lower alkanes, said catalysts being suitable for usein vapor phase oxidative dehydrogenation of C₂-C₅ lower alkanes in thepresence of molecular oxygen to produce corresponding olefins andcharacterized by having a composition expressed by a general formula (I)below:

Mn_(α)E¹ _(β)E² _(γ)Ox  (I)

[0010] (in which Mn denotes manganese, and O, oxygen; E¹ is at least oneelement selected from the group consisting of P, As, Sb, B, S, Se, Te,F, Cl, Br, I, Nb, Ta, W, Re and Cu; E² is at least one element selectedfrom the group consisting of Cr, Fe, Co, Ni, Ag, Au, Zn, Tl, Sn, Pb, Bi,Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Y, La, Ce, Nd and Sm; and α, β, γ andx denote atomic numbers of Mn, E¹, E² and oxygen, respectively, wherewhen α=1, β=0.01-10, γ=0-5, and x is a numerical value determined by thestate of oxidation of those elements other than oxygen).

[0011] The present invention furthermore provides a process forproducing olefins which comprises vapor phase oxidative dehydrogenationof C₂-C₅ alkanes in the presence of molecular oxygen to formcorresponding olefins, characterized by the use of the above-describedcatalyst.

[0012] According to the present invention, furthermore, a process forproducing, from lower alkane, unsaturated aldehyde and unsaturated acidat high yield is provided, in which an olefin obtained throughvapor-phase oxidative dehydrogenation of C₂-C₅ lower alkanes in thepresence of molecular oxygen using the above-defined catalyst is furtheroxidized at vapor phase in the presence of oxygen to provide unsaturatedaldehyde and unsaturated acid.

[0013] The invention moreover provides a process for producingunsaturated acid from lower alkane at high yield, in which theunsaturated aldehyde obtained as above is further oxidized at vaporphase in the presence of molecular oxygen to provide unsaturated acid.

EMBODIMENTS OF THE INVENTION

[0014] More specifically, C₂-C₅ lower alkanes signify ethane, propane,n-butane, isobutane, n-pentane and isopentane. The catalysts of thepresent invention are used in oxidative dehydrogenation reactions ofthese lower alkanes to produce corresponding olefins, more specifically,ethylene from ethane, propylene from propane, n-butene from n-butane,isobutene from isobutane, n-pentene from n-pentane and isopentene fromisopentane. These lower alkanes may be used either singly or as amixture of more than one. The oxidative dehydrogenation catalysts of thepresent invention are useful for the production of, in particular,propylene and isobutene from propane and isobutane, respectively.

[0015] Referring to the general formula (I), the catalysts in which,when α=1, β=0.02-2, and γ=0-1 are particularly preferred.

[0016] For improving the selectivity for, and yield of, the product, thecatalysts of the general formula (I) in which E¹ component is P, Sb, B,S, Nb, W or Re and E² component is Cr, Fe, Sn, Na, Mg or Ce arepreferred.

[0017] The oxidative dehydrogenation catalysts of general formula (I) ofthe present invention may be used as supported on a refractory inorganiccarrier for the purpose of improving activity level and physicaldurability. As the refractory inorganic carrier, those generally used inpreparation of this type of catalysts can be used, the representativeexamples thereof including silica, alumina, titania, zirconia,silica-alumina, silica-titania and silica-zirconia. In particular,silica and silica-alumina are preferred, because they give higher yieldof object products. The ratio of silica in the silica-alumina catalystsystem normally ranges from 10% by weight to less than 100% by weight.The amount of the catalytically active component to be carried isnormally between 10 and 90% by weight of the refractory inorganiccarrier.

[0018] The method of preparation of the oxidative dehydrogenationcatalysts of the present invention is not subject to any criticallimitations, but any of conventionally practiced methods or knownmethods for preparation of this type of catalysts can be used. Forexample, the catalysts may be prepared by the procedures comprisingadding to a slurry of manganese dioxide powder antimony trioxide powderand aqueous solutions of phosphoric acid, boric acid, ammonium sulfate,telluric acid, ammonium chloride, niobium oxalate, ammonium tungstate,rhenium oxide and copper nitrate, etc. as E¹ component; if necessaryfurther adding aqueous solution of at least one element selected fromthe E² component; further if necessary adding a carrier such as silica,alumina or the like thereto; condensing the mixture under heating withagitation for a prescribed period, drying the resultant paste at 80-300°C.; pulverizing and molding the same; if necessary further crushing thesame for size adjustment or re-drying at 80-300° C.; and if necessaryfurther firing the dry product at 300-800° C. The firing atmosphere issubject to no limitation, and the firing may be conducted in air, anatmosphere of high or low oxygen concentration, a reducing atmosphere,in an inert gas such as nitrogen, helium, argon or the like, or invacuum. In most desirable practice, the catalyst is not firing at thehigh temperatures but is contacted with the reaction gas containing thealkane or alkanes and oxygen as it has undergone the drying treatment ortreatments at not higher than 300° C. In that occasion, the reaction maybe started at a temperature not lower than the prescribed level by wayof a pre-treating reaction, or directly at the prescribed temperature.In the latter case changes in catalytic activity may be observed at theinitial stage of the reaction, but normally a stable activity level isreached within an hour.

[0019] The starting materials for catalyst preparation are not critical,but may be any of nitrate, sulfate, oxide, hydroxide, chloride,carbonate, acetate, oxygen acid, ammonium salt of oxygen acid, etc. ofthe elements.

[0020] As Mn source, besides powders of various oxides thereof or moldedproducts which are useful as they are, manganese hydroxide slurriesobtained upon treating an aqueous solution of, eg., manganese nitrate,with aqueous ammonia or the like are conveniently used. Any means usedfor catalyst preparation in general, for example, co-precipitation of amanganese compound with compounds of other additive elements from theiraqueous solution, are applicable. As sulfur source, aqueous sulfuricacid or ammonium sulfate may be used, or the whole or a part thereof maybe introduced in the form of sulfate(s) of other additive element(s).Similarly, halogen may be introduced as aqueous hydrogen halide orammonium halide, or in the form of halide(s) of other additiveelement(s).

[0021] Again the use form of refractory inorganic carrier is subject tono critical limitation, which allows versatile selection according tothe form of use of the catalyst, such as, besides molded products,powder of oxide or hydroxide, gel or sol.

[0022] The starting gas to be subjected to the vapor phase oxidativedehydrogenation reaction according to the present invention may ifnecessary contain a diluent gas, besides lower alkane(s) and molecularoxygen. As the molecular oxygen, air or pure oxygen is used, normally ata ratio of 0.1-5 mols per mol of alkane. As the diluent gas, an inertgas such as nitrogen, helium or carbon dioxide or steam is convenientlyused.

[0023] The reaction conditions for carrying out the vapor phaseoxidative dehydrogenation of the present invention are subject to nocritical limitation. For example, the starting gas as described above iscontacted with an oxidative dehydrogenation catalyst of the presentinvention under such conditions as: at a space velocity of 300-30,000hr⁻¹ at a temperature between 250 and 650° C. While the reaction isnormally conducted under atmospheric pressure, a reduced or elevatedpressure may be used. The reaction system again is not critical, whichmay be a fixed bed system, moving bed system or fluidized bed system. Itmay also be one-pass system or recycling system.

[0024] The olefines (alkenes) which are obtained through the vapor phaseoxidative dehydrogenation of C₂-C₅ lower alkanes (alkane oxidativedehydrogenation step) using the catalyst of the present invention can befurther oxidized to produce unsaturated aldehydes and unsatuated acids(alkene oxidation step). The unsaturated aldehydes can further beoxidized to produce unsaturated acids (aldehyde oxidation step). Thusformed unsaturated aldehydes and/or unsaturated acids are trapped withan absorption column (absorbing step). As the oxygen source in thepresent invention, air and/or oxygen produced by such methods ascryogenic method, P.S.A. (pressure swing adsorption) method and the likecan be used. According to the present invention, it is possible to formfrom lower alkanes the corresponding olefins, without side-production ofhydrogen. If necessary oxygen and/or steam may be added to the gases tobe introduced in each of the above steps, and such additional oxygenand/or steam are supplied by, for example, air, above-described oxygen,water and/or the gas discharged of said absorbing step.

[0025] As one specific example of useful catalyst in the alkeneoxidation step, those expressed by following general formula (2) may benamed:

Mo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)  (2)

[0026] in which Mo is molybdenum; Bi is bismuth; Fe is iron; A is atleast one element selected from the group consisting of cobalt andnickel; B is at least one element selected from the group consisting ofalkali metals and thallium; C is at least one element selected from thegroup consisting of silicon, aluminium, zirconium and titanium; D is atleast one element selected from the group consisting of tungsten,phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese,arsenic and zinc; and O is oxygen: and the ratio of those elements is,when a=12, b=0.1-10, c=0.1-20, d=2-20, e=0.001-10, f=0-30, g=0-4 and xis a numerical value determined by the state of oxidation of thoseelements other than oxygen.

[0027] Also as one specific example of useful catalyst in the aldehydeoxidation step, those expressed by following general formula (3) may benamed:

Mo_(h)V_(i)W_(j)E_(k)F_(l)G_(m)H_(n)O_(x)  (3)

[0028] in which Mo is molybdenum; V is vanadium; W is tungsten; E is atleast one element selected from the group consisting of copper, cobalt,bismuth and iron; F is at least one element selected from the groupconsisting of antimony and niobium; G is at least one element selectedfrom the group consisting of silicon, aluminium, zirconium and titanium;H is at least one element selected from the group consisting of alkalineearth metals, thallium, phosphorus, tellurium, tin, cerium, lead,manganese and zinc; and O is oxygen: and the ratio of those elements is,when h=12, i=0.1-10, j=0-10, k=0.1-20, l=0-10, m=0-10, n=0-30, and x isa numerical value determined by the state of oxidation of those elementsother than oxygen.

EFFECT OF THE INVENTION

[0029] The lower alkane oxidative dehydrogenation catalysts according tothe present invention excel in the oxidative dehydrogenation ability andenable the production from lower alkanes of corresponding olefins athigh yield.

[0030] Furthermore, due to their higher activity level than that ofknown catalyst system, the amount of the catalyst necessary for securingthe same level of STY (space time yield) is far less than that ofconventional catalysts, such as from ⅓to {fraction (1/10)}.

[0031] Also according to the present invention, unsaturated aldehydeand/or unsaturated acid can be produced from lower alkanes stably athigh yield.

EXAMPLES

[0032] Hereinafter the invention is explained in further detailsreferring to working examples, in which percentage are by weight, unlessotherwise specified, and the conversion, one-pass yield and selectivityare indicated following the definitions below, inclusive of the sideproducts:${{conversion}\quad \left( {{mol}\quad \%} \right)} = {\frac{\left( {{mol}\quad {number}\quad {of}\quad {reacted}\quad {alkane}} \right)}{\left( {{mol}\quad {number}\quad {of}\quad {fed}\quad {alkane}} \right)} \times 100}$${{selectivity}\quad \left( {{mol}\quad \%} \right)} = {\frac{\left( {{mol}\quad {number}\quad {of}\quad {each}\quad {of}\quad {formed}\quad {compounds}} \right)}{\left( {{mol}\quad {number}\quad {of}\quad {reacted}\quad {alkane}} \right)} \times \frac{\left( {{carbon}\quad {number}\quad {of}\quad {each}\quad {of}\quad {formed}\quad {compounds}} \right)}{\left( {{carbon}\quad {number}\quad {of}\quad {fed}\quad {alkane}} \right)} \times 100}$${{one}\text{-}{pass}\quad {yield}\quad \left( {{mol}\quad \%} \right)} = {{\frac{\left( {{mol}\quad {number}\quad {of}\quad {each}\quad {of}\quad {formed}\quad {compounds}} \right)}{\left( {{mol}\quad {number}\quad {of}\quad {fed}\quad {alkane}} \right)} \times \frac{\left( {{carbon}\quad {number}\quad {of}\quad {each}\quad {of}\quad {formed}\quad {compounds}} \right)}{\left( {{carbon}\quad {number}\quad {of}\quad {fed}\quad {alkane}} \right)} \times 100} = \frac{{conversion} \times {selectivity}}{100}}$

Example 1

[0033] Into a 500-ml beaker, 4.35 g of manganese dioxide powder(MnO₂,Kishida Chemical, purity 99.9%) and 200 ml of water were fed and heatedunder agitation. Further 1.09 g of antimony trioxide powder (Wako PureChemical Industry LTD., purity 99.9%) was added to the system which wasthen heated to about 80° C., and stirred for 2 hours while beingmaintained at a constant liquid volume. Then the temperature was raisedto 90° C. and stirring was continued for about 4 hours allowingconcentration by evaporation of water content. The resulting paste wasdried for 14 hours at 120° C., pulverized, molded and crushed touniformize the size to 9-20 mesh. The resulting catalyst had acomposition of Mn₁Sb_(0.15)Ox, 0.6 g of which was charged in an ordinaryflow type reactor. The reaction was conduced under the followingconditions;

[0034] Reaction gas: C₃H₈/O₂/N₂=1/1/8 (molar ratio)

[0035] Feed rate: 112.5 ml/min.

[0036] SV: equivalent to 12,000 hr⁻¹ (In the subsequent Examples,indication of SV is omitted. As the catalyst weight was constant, SVunderwent fluctuation more or less dependent on its packing density.)

[0037] Reaction temperature: 450° C.

[0038] The results were as shown in Table 1.

Example 2

[0039] The catalyst preparation was conducted in the same manner as inExample 1, except that the amount of the antimony trioxide powder waschanged to 1.82 g. The resulting catalyst had a composition ofMn₁Sb_(0.25)Ox. Using 0.6 g of this catalyst, the reaction was conductedunder identical conditions with those of Example 1. The results were asshown in Table 1.

Example 3

[0040] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with0.58 g of 85% phosphoric acid (H₃PO₄, special grade reagent manufacturedby Kanto Chemical) as dissolved in 50 ml of water. The resultingcatalyst had a composition of Mn₁P_(0.1)Ox. Using 0.6 g of thiscatalyst, the reaction was conducted under identical conditions withthose of Example 1, except that the reaction temperature was raised to490° C. The results were as shown in Table 1.

Example 4

[0041] The catalyst preparation was conducted in the same manner as inExample 3, except that the amount of the 85% phosphoric acid was changedto 1.15 g. The resulting catalyst had a composition of Mn₁P_(0.2)Ox.Using 0.6 g of this catalyst, the reaction was run under identicalconditions with those of Example 3. The results were as shown in Table1.

Example 5

[0042] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with0.31 g of boric acid (H₃BO₃, special grade reagent manufactured by KantoChemical) as dissolved in 50 ml of water. The resulting catalyst had acomposition of Mn₁B_(0.1)Ox. Using 0.6 g of this catalyst, the reactionwas run under identical conditions with those of Example 3. The resultswere as shown in Table 1.

Example 6

[0043] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with0.66 g of ammonium sulfate (special grade reagent manufactured by KantoChemical) as dissolved in 50 ml of water. The resulting catalyst had acomposition of Mn₁S_(0.1)Ox. Using 0.6 g of this catalyst, the reactionwas run under identical conditions with those of Example 3. The resultswere as shown in Table 1.

Example 7

[0044] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.62 g of niobium oxalate (a product of C.B.M.M. Co., containing 20.5%of Nb₂O₅ upon conversion) as dissolved in 100 ml of water. The resultingcatalyst had a composition of Mn₁Nb_(0.05)Ox. Using 0.6 g of thiscatalyst, the reaction was run under identical conditions with those ofExample 3. The results were as shown in Table 1.

Example 8

[0045] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.16 g of aqueous ammonium meta-tungstate solution, MW-2 (a product ofNippon Inorganic Colour and Chemical Co., LTD., containing 50% of WO₃)as diluted with 50 ml of water. The resulting catalyst had a compositionof Mn₁W_(0.05)Ox. Using 0.6 g of this catalyst, the reaction was rununder identical conditions with those of Example 3. The results were asshown in Table 1.

Example 9

[0046] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with0.61 g of rhenium oxide (Re₂O₇, Kishida Chemical, purity 99.99%) asdissolved in 50 ml of water. The resulting catalyst had a composition ofMn₁Re_(0.05)Ox. Using 0.6 g of this catalyst, the reaction was run underidentical conditions with those of Example 3. The results were as shownin Table 1.

Example 10

[0047] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.21 g of copper nitrate (Wako Pure Chemical Industry LTD., purity99.9%) as dissolved in 50 ml of water. The resulting catalyst had acomposition of Mn₁Cu_(0.1)Ox. Using 0.6 g of this catalyst, the reactionwas run under identical conditions with those of Example 3. The resultswere as shown in Table 1.

Example 11

[0048] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.07 g of ammonium chloride (special grade reagent manufactured by KantoChemical) as dissolved in 50 ml of water. The resulting catalyst had acomposition of Mn₁Cl_(0.4)Ox. Using 0.6 g of this catalyst, the reactionwas run under identical conditions with those of Example 3. The resultswere as shown in Table 1.

Example 12

[0049] The catalyst preparation was conducted in the same manner as inExample 1, except that 2.00 g of chromium nitrate [Cr(NO₃)₃.9H₂O, WakoPure Chemical Industry LTD., purity 99.9%] as dissolved in 50 ml ofwater was added following the addition of the antimony trioxide powder.The resulting catalyst had a composition of Mn₁Sb_(0.15)Cr_(0.1)Ox.Using 0.6 g of this catalyst, the reaction was run under identicalconditions with those of Example 1. The results were as shown in Table1.

Example 13

[0050] The catalyst preparation was conducted in the same manner as inExample 1, except that 2.02 g of iron nitrate [Fe(NO₃)₃.9H₂O, Wako PureChemical Industry LTD., special grade reagent] as dissolved in 50 ml ofwater was added following the addition of the antimony trioxide powder.The resulting catalyst had a composition of Mn₁Sb_(0.15)Fe_(0.1)Ox.Using 0.6 g of this catalyst, the reaction was run under identicalconditions with those of Example 1. The results were as shown in Table1.

Example 14

[0051] The catalyst preparation was conducted in the same manner as inExample 1, except that 0.42 g of sodium nitrate (Wako Pure ChemicalIndustry LTD., special grade reagent) as dissolved in 50 ml of water wasadded following the addition of the antimony trioxide powder. Theresulting catalyst had a composition of Mn₁Sb_(0.15)Na_(0.1)Ox. Using0.6 g of this catalyst, the reaction was run under identical conditionswith those of Example 1. The results were as shown in Table 1.

Example 15

[0052] The catalyst preparation was conducted in the same manner as inExample 1, except that 1.28 g of magnesium nitrate [Mg(NO₃)₂.6H₂O, WakoPure Chemical Industry LTD., special grade reagent] as dissolved in 50ml of water was added following the addition of the antimony trioxidepowder. The resulting catalyst had a composition ofMn₁Sb_(0.15)Mg_(0.1)Ox. Using 0.6 g of this catalyst, the reaction wasrun under identical conditions with those of Example 1. The results wereas shown in Table 1.

Example 16

[0053] The catalyst preparation was conducted in the same manner as inExample 1, except that 2.22 g of cerium nitrate [Ce(NO₃)₃.6H₂O, WakoPure Chemical Industry LTD., special grade reagent, purity 98%] asdissolved in 50 ml of water was added following the addition of theantimony trioxide powder. The resulting catalyst had a composition ofMn₁Sb_(0.15)Ce_(0.1)Ox. Using 0.6 g of this catalyst, the reaction wasrun under A identical conditions with those of Example 1. The resultswere as shown in Table 1.

Example 17

[0054] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.11 g of chromium sulfate [Cr₂(SO₄)₃.4H₂O, Kanto Chemical, first gradereagent] as dissolved in 50 ml of water. The resulting catalyst had acomposition of Mn₁S_(0.15)Cr_(0.1)Ox. Using 0.6 g of this catalyst, thereaction was run under identical conditions with those of Example 3. Theresults were as shown in Table 1.

Example 18

[0055] The catalyst preparation was conducted in the same manner as inExample 1, except that the antimony trioxide powder was replaced with1.75 g of stannic chloride (SnCl₄.5H₂O, Wako Pure Chemical Industry.LTD., special grade reagent) as dissolved in 50 ml of water. Theresulting catalyst had a composition of Mn₁Cl_(0.4)Sn_(0.1)Ox. Using 0.6g of this catalyst, the reaction was run under identical conditions withthose of Example 3. The results were as shown in Table 1.

Example 19

[0056] The catalyst preparation was conducted in the same manner as inExample 1, except that 1.16 g of aqueous ammonium meta-tungstatesolution MW-2 as diluted with 50 ml of water and 2.00 g of chromiumnitrate as dissolved in 50 ml of water were added following the additionof the antimony trioxide powder. The resulting catalyst had acomposition of Mn₁Sb_(0.15)W_(0.05)Cr_(0.1)Ox. Using 0.6 g of thiscatalyst, the reaction was run under identical conditions with those ofExample 1. The results were as shown in Table 1.

Example 20

[0057] Using 0.6 g of the catalyst which was used in Example 19, thereaction of Example 19 was repeated except that the reaction temperaturewas raised to 490° C. The results were as shown in Table 1.

Example 21

[0058] The catalyst preparation was conducted in the same manner as inExample 1, except that 1.16 g of aqueous ammonium meta-tungstatesolution as diluted with 50 ml of water and 1.11 g of chromium sulfateas dissolved in 50 ml of water were added following the addition of theantimony trioxide powder. The resulting catalyst had a composition ofMn₁Sb_(0.15)W_(0.05)S_(0.15)Cr_(0.1)Ox. Using 0.6 g of this catalyst,the reaction was run under identical conditions with those of Example 3.The results were as shown in Table 1.

Example 22

[0059] Using 0.6 g of this catalyst which was used in Example 21, thereaction of Example 21 was repeated except that the reaction temperaturewas raised to 530° C. The results were as shown in Table 1.

Example 23

[0060] The catalyst preparation was repeated except that 1.16 g ofaqueous ammonium meta-tungstate solution MW-2 as diluted with 50 ml ofwater, 1.62 g of niobium oxalate as dissolved in 100 ml of water and2.00 g of chromium nitrate as dissolved in 50 ml of water were addedfollowing the addition of the antimony trioxide powder. The resultingcatalyst had a composition of Mn₁Sb_(0.15)W_(0.05)Nb_(0.05)Cr_(0.1)Ox.Using 0.6 g of this catalyst, the reaction was run under identicalconditions with those of Example 3. The results were as shown in Table1.

Example 24

[0061] Using 0.6 g of the same catalyst as used in Example 23, thereaction of Example 23 was repeated except that the reaction temperaturewas raised to 530° C. The results were as shown in Table 1.

Comparative Example 1

[0062] The same manganese dioxide powder as the one used in Example 1was pulverized, molded and crushed to a uniform size of 9-20 mesh. Using0.6 g of this catalyst, the reaction was run under identical conditionswith those of Example 1. The results were as shown in Table 1.

Comparative Example 2

[0063] The reaction of Example 1 was repeated except that 0.6 g thecatalyst same to that used in Comparative Example 1 was used and thereaction temperature was raised in 490° C. The results were as shown inTable 1.

Example 25

[0064] Using isobutane instead of propane, isobutene was synthesized,assisted by the same catalyst as the one used in Example 19. An ordinaryflow type reactor was charged with 0.6 g of the catalyst of 9-20 mesh insize, and through which a reaction gas composed of i-C₄H₁₀/O₂/N₂=1/1/8(molar ratio) was passed at a rate of 112.5 ml/min. The reactiontemperature was 450° C. The results were: isobutane conversion 26.5%,isobutene selectivity 27.5%, methacrolein selectivity 0.9% and one-passyield of isobutene 7.3%. TABLE 1 Propane Reaction Con- One-Pass Temp.version Selectivity (%) Yield (%) (° C.) (%) Propylene AcroleinPropylene Example 1 450 27.3 27.1 0.3 7.4 Example 2 450 26.9 26.7 0.77.2 Example 3 490 31.2 33.4 0.3 10.4 Example 4 490 30.9 33.7 0.3 10.4Example 5 490 9.7 47.3 1.4 4.6 Example 6 490 17.9 36.3 0.4 6.5 Example 7490 30.3 29.6 0.2 9.0 Example 8 490 29.7 29.4 0.2 8.7 Example 9 490 8.453.8 0.2 4.5 Example 10 490 25.3 22.2 0.1 5.6 Example 11 490 27.1 16.10.1 4.4 Example 12 450 30.0 28.0 0.5 8.4 Example 13 450 28.1 27.8 0.67.8 Example 14 450 26.5 28.7 0.3 7.6 Example 15 450 27.4 28.1 0.3 7.7Example 16 450 29.2 26.7 0.4 7.8 Example 17 490 28.8 23.8 0.1 6.9Example 18 490 25.5 19.8 0.1 5.0 Example 19 450 29.8 35.2 0.1 10.5Example 20 490 32.8 37.9 0.3 12.4 Example 21 490 31.6 42.9 2.0 13.6Example 22 530 36.5 42.6 1.8 15.5 Example 23 490 33.6 39.9 0.7 13.5Example 24 530 35.5 41.7 0.8 14.8 Comparative 450 18.0 10.5 0 1.9Example 1 Comparative 490 23.7 13.4 0 3.2 Example 2

Example 26

[0065] Each independently temperature-controllable single-pipe flow typereactors (A), (B) and (C) were connected in such a manner that gas wouldflow by the order of (A) to (B) to (C), with the piping so designed thatthe gas formed in the reactor (C) is introduced into an absorptioncolumn to allow absorption of condensed component and introduction ofthe uncondensed gas flowing out of the absorption column into thereactor A through its gas inlet portion, and the reaction was conductedwith the following particulars. The piping also was so connected thatfresh air could be introduced into the reactor (B) through its gas inletportion.

[0066] (Preparation of Catalyst)

[0067] 9 g of the catalyst as used in Example 21 was packed in thereactor (A), while the reactor (B) was packed with 32 g of a catalyst ofthe following composition (excepting oxygen) as described in Example 1of Japanese Patent Publication No. 42241/1972:

Mo₁₀Co₄Bi₁Fe₁W₂Si_(1.35)K_(0.05).

[0068] The reactor (C) was packed with 52 g of a catalyst of thefollowing composition (excepting oxygen) as described in Example 1 ofJapanese KOKAI No. 206504/1996:

Mo₁₂V_(6.1)W₁Cu_(2.3)Sb_(1.2).

[0069] The flow rates of propane, air and recovered gas from absorptioncolumn were so controlled at the gas inlet portion of the reactor (A) asto give the reaction gas composition of 15 vol % C₃H₈, 15 vol % O₂ and70 vol % of inert gases comprising nitrogen, carbon oxide, etc. In thatoccasion, the space velocity to the oxidative dehydrogenation catalystwas 3000 hr⁻¹. The product gas from the reactor (A) was fed into thereactor (B) while adding air thereto at such a rate that O₂/C₃H₆ ratiotherein should become 2.5 at the entrance portion of the reactor (B),and the product gas from the reactor (B) was fed into the reactor (C).The reaction temperatures in the reactors (A), (B) and (C) during therun were 480° C., 325° C. and 250° C., respectively.

[0070] Analysis of the product gas from the reactor (C) indicated: C₃H₈conversion, 45.5 mol % and acrylic acid yield, 20.7 mol %.

Example 27

[0071] To the reactor assembly used in Example 26, piping was connectedto allow introduction of fresh air and steam into the gas inlet portionof the reactor (C), and the reaction was carried out with theparticulars as follows.

[0072] The flow rates of propane and gaseous oxygen were so controlledat the gas inlet portion of the reactor (A) as to give the reaction gascomposition of 30 vol % C₃H₈, 30 vol % O₂ and 40 vol % of inert gasescomprising nitrogen, carbon oxide, etc. The space velocity to theoxidative dehydrogenation catalyst in that occasion was 4,000 hr⁻¹. Theproduct gas from the reactor (A) was fed into the reactor (B) whileadding air thereto at such a rate that the O₂/C₃H₆ ratio therein shouldbecome 1.5 at the gas inlet portion of the reactor (B). The product gasfrom the reactor (B) was fed into the reactor (C), while adding air andsteam thereto at such rates that the O₂/acrolein ratio and steamconcentration therein should become 1.3 and 35 vol %, respectively, atthe gas inlet portion of the reactor (C). Other conditions wereidentical with those of Example 26.

[0073] Analysis of the product gas from the reactor (C) indicated: C₃H₈conversion, 44.1 mol % and acrylic acid yield, 20.1 mol %.

1. Oxidative dehydrogenation catalysts for lower alkanes, said catalystsbeing suitable for use in vapor phase oxidative dehydrogenation of C₂-C₅lower alkanes in the presence of molecular oxygen to producecorresponding olefins and characterized by having a compositionexpressed by a general formula (I) below: Mn_(α)E¹ _(β)E² _(γ)Ox  (I)(in which Mn denotes manganese, and I, oxygen; E¹ is at least oneelement selected from the group consisting of P, As, Sb, B, S, Se, Te,F, Cl, Br, I, Nb, Ta, W, Re and Cu; E² is at least one element selectedfrom the group consisting of Cr, Fe, Co, Ni, Ag, Au, Zn, Tl, Sn, Pb, Bi,Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Y, La, Ce, Nd and Sm; and α, β, γ andx denote atomic numbers of Mn, E¹, E² and oxygen, respectively, wherewhen α=1, β=0.01-10, γ=0-5, and x is a numerical value determined by thestate of oxidation of those elements other than oxygen).
 2. Thecatalysts as described in claim 1 , in which, referring to the generalformula (I), when α=1, β=0.02-2 and γ=0-1.
 3. The catalysts as describedin claim 1 or 2 , in which S as E¹ is added in the form of sulfate ion(SO₄ ²⁻).
 4. The catalysts as described in claim 3 , in which thesulfate ion is added in the form of a sulfate.
 5. The oxidativedehydrogenation catalysts as described in any one of claims 1-4, inwhich the preparation process of the catalysts includes drying attemperatures not higher than 300° C. only, and does not include firingat high temperatures exceeding 300° C.
 6. A process for producingolefins which comprises oxydizing and dehydrogenating C₂-C₅ loweralkanes in the presence of molecular oxygen at vapor phase to producecorresponding olefins, characterized in that a catalyst as described inclaim 1 is used.
 7. A process for producing unsaturated aldehyde andunsaturated acid from lower alkane which comprises oxidizing an olefinwhich has been obtained through vapor-phase oxidative dehydrogenation ofC₂-C₅ lower alkane in the presence of molecular oxygen using a catalystas described in claim 1 , at vapor phase in the presence of oxygen toproduce unsaturated aldehyde and unsaturated acid.
 8. A process forproducing unsaturated acid from lower alkane, which comprises oxidizingat vapor phase the unsaturated aldehyde as obtained according to claim 7in the presence of molecular oxygen to produce unsaturated acid.